1. Field of the Invention
The present invention relates to a transfer arm, employed in a semiconductor processing system or the like, which is capable of accurately transferring substrates and which has excellent durability and thus long life.
2. Description of the Prior Art
Generally employed in a semiconductor processing system is a substrate transfer apparatus for transferring target substrates such as semiconductor wafers by predetermined sequence control. Such a substrate transfer apparatus is required to operate with its high accurate movement in a clean operational environment where airborne particles such as dust do not exist.
FIG. 27 is a schematic structural view schematically showing the structure and the operation of conventional transfer arms of a substrate transfer apparatus (see Japanese Patent No. 2808826). In the transfer apparatus, transfer arms shown in FIG. 27 each comprise two pairs of parallel link elements (two parallel links) connected by a common short link element allowing the folding and stretching of the arm. The folding and stretching of the arm achieves linear reciprocating motion of a substrate holder to transfer a substrate (not shown) in the longitudinal direction. To prevent occurrence of interference between the pairs of parallel link elements, one pair of parallel link elements are disposed at a level different from the level of the other pair of parallel link elements. The two transfer arms are arranged symmetrically relative to the center line. By this structure, continuous transfer is achieved.
As shown in FIG. 27, in a conventional mechanism of the transfer apparatus 500, articulated arms 520, 530 are arranged symmetrically relative to a center line C. Each of the arms 520, 530 comprises a linkage in which a parallel link 540 has link elements 541, 542 as long link elements, a parallel link 550 has link elements 551, 552 as long link elements, and two gears 570, 572 engaging each other compose a short link element common to both the parallel link 540 and the parallel link 550. The gear 570 is fixed to the link element 542 and the gear 572 is fixed to the link element 552.
A short link element 543 for the link elements 541, 542 at the opposite side of the common short link element is mounted on a rotary stand 510 as a drive. A substrate holder 590 is disposed on a short link element 553 connected to the other ends of the link elements 551, 552.
In the transfer apparatus 500 structured as mentioned above, the arm 530 is shown in its initial state. As the parallel link 540 is swung by rotation of a rotary shaft R50. Because of the engagement of the gears 570 and 572, the parallel link 550 is swung in a direction opposite to and at the same angle as the swing motion of the parallel link 540. As a result, the arm 520 shown in the right half of FIG. 27 linearly moves the substrate holder 590 in the direction of arrow A along the center line C, while increasing the angle of a V shape formed between the two parallel links after passing the position on the rotary shaft R50.
Instead of the two gears 570, 572 composing the short link element, a pulley belt or a wire may be employed as a mechanism for the folding and stretching of the arm composed of the two parallel links.
However, since gears to be engaged should be designed to have a predetermined backlash between them, the linkage easily rattles during the movement. This reduces the precision of transfer, so there is a problem that high precision of positioning can not be expected. There is also another problem that powders are produced by the grinding between teeth of the gears. On the other hand, in a conventional example in which the synchronization in moving angle is achieved by pulleys and a steel belt or a wire wound around the pulleys, there is a possibility of early causing of fatigue failure because the folding of the belt or wire is frequently repeated for being wound onto the pulleys. The life of the belt or wire is defined by the tension and the fold radius when the belt or wire is wound. For this, increase in the diameter of the pulley to be employed is considered as one of solving means. However, in this case, increase of the diameter of the pulley makes it difficult to miniaturize the apparatus as a whole.
In case where substrates are processed under high temperature condition, the belt or wire should be early deformed and deteriorated, so there is also a problem of durability.
Therefore, the first object of the present invention is to provide a transfer arm which can solve the aforementioned problems of the prior art, which is capable of accurately transferring substrates, and which has excellent durability because the wearing of components can be minimized.
The second object of the present invention is to provide a transfer arm which can solve the aforementioned problems of the prior art, which is capable of accurately transferring substrates under high temperature condition, and which has excellent durability because the wearing of components can be minimized.
For achieving the above first object, the present invention provides, as a first embodiment (described later), a transfer arm having a first parallel link and a second parallel link which are connected to each other by a common short link element, a drive shaft at an end of a link element of said first parallel link, and a holding plate disposed on the free end of said second parallel link which is linearly moved according to the rotation of said drive shaft while deforming parallelograms formed by the link elements of said first parallel link and formed by the link elements of said second parallel link, said transfer arm being characterized by comprising a linear guide having a guide rail disposed on a base between said first parallel link and said second parallel link to extend in a direction perpendicular to said common short link, and a synchronous link for connecting a slider which is slidable on said guide rail, articular shafts supporting the ends of link elements of said first parallel link, and articular shafts supporting the ends of link elements of said second parallel link which are arranged symmetrically relative to said linear guide.
It is preferable that said slider of said linear guide is linearly moved by the swing motion of the link element(s) of the first parallel link, and the link elements of the second parallel link are swung in a direction opposite to and at the same angle as the swing motion of the link elements of said first parallel link via said synchronous link according to the linear movement of said slider, whereby the holding plate disposed on the free end of said second parallel link is linearly moved while varying the angle formed between the link elements of said first parallel link and the link elements of said second parallel link.
It is preferable that said transfer arms are arranged to be opposed to each other relative to a center line parallel to the direction of transferring said holding plate, whereby subject objects are continuously transferred by alternatively operating the folding and stretching of said transfer arms.
It is preferable that said pair of transfer arms comprise two drive shafts which are coaxially arranged to allow independent folding and stretching operation of the respective transfer arms.
The present invention provides a transfer arm comprising two drive shafts coaxially arranged one of which is connected to an end of a link element of a quadrate link and the other one of which is connected to an end of another link element of the quadrate link which is symmetrical relative to a center line, a linear guide which is positioned at a joint of the other ends of the link elements at a location opposite to the location of said drive shaft, and a synchronous link which is arranged between a slider of said linear guide and portions near the ends of said link elements which are opposite to the ends connected to said joint.
In this case, it is preferable that said joint of the link elements of said quadrate link is linearly moved along said center line by turning said two drive shafts in the opposite directions at the same angular rate.
In addition, the entire of said quadrate link can be swung at a predetermined angle about said drive shaft by turning said two drive shafts in the same direction at the same angular rate.
The transfer arm of the present invention which can accomplish the first object exhibits effects of accurately transferring substrates and keeping clean operational environment because of little wearing of components so as to obtain excellent durability.
For achieving the above second object, the present invention provides, as from second to forth embodiments (described later), a transfer arm having a first parallel link and a second parallel link which are connected to each other by a common short link element, a drive shaft at an end of a link element of said first parallel link, and a holding plate disposed on the free end of said second parallel link which is linearly moved according to the rotation of said drive shaft while deforming parallelograms formed by the link elements of said first parallel link and formed by the link elements of said second parallel link, said transfer arm being characterized by comprising a linear guide extending in a direction perpendicular to a short link element including said drive shaft, wherein one of the link element of said second parallel link has an extension, which end is rotatably connected to a slider which linearly moves along the linear guide.
It is preferable that said linear guide has an end fixed to a base plate functioning as said common short link element.
It is preferable that said linear guide has an end fixed to an intermediate plate disposed to said first parallel link in parallel with said short link element of said first parallel link.
A transfer arm is having a lever having an end connected to a drive shaft, a parallel link composed of two link elements and two short link elements, the other end of said lever being connected to a middle point of one of said link elements, and a holding rod disposed on one of said short link elements, wherein said holding rod is linearly moved in a predetermined transferring direction via said lever while transforming parallelograms formed by the link elements of said parallel link, said transfer arm being characterized by further comprising a linear guide extending in a direction perpendicular to the transferring direction of said holding rod, and a slider which linearly moves along said linear guide, wherein said slider and a portion of the other one of said short link elements are formed as one unit.
It is preferable that said lever length is a half of the length of the link element of said parallel link and said lever is connected to the center in the longitudinal direction of said link element of said parallel link.
The present invention also provides a transfer arm having a first parallel link and a second parallel link which are connected to each other by a common short link element, a drive shaft at an end of a link element of said first parallel link, and a holding plate disposed on the free end of said second parallel link which is linearly moved according to the rotation of said drive shaft while deforming parallelograms formed by the link elements of said first parallel link and formed by the link elements of said second parallel link, said transfer arm being characterized by comprising linear guides which extend in a direction perpendicular to a short link element including said drive shaft and are arranged symmetrically relative to said drive shaft, a guide rod of which one end is connected to an intermediate position of said second parallel link, and a rod which is connected to an intermediate position of said guide rod and extends in parallel with the link elements of said second parallel link, wherein the other end of said guide rod is rotatably connected to one of sliders which linearly move along said linear guides and an end of said rod is rotatably connected to the other one of the sliders so as to form isosceles-triangular links which are arranged symmetrically relative to said drive shaft and of which summits are composed of a common point at the drive shaft and base sides are said linear guides, respectively.
It is also preferable that, instead of the isosceles-triangular links, the transfer arm being characterized by comprising a linear guide extending in a direction perpendicular to a short link element including said drive shaft and a guide rod of which one end is connected to a portion of the link element of said second parallel link, wherein the other end of said guide rod is rotatably connected to a slider which linearly moves along the linear guide so as to form a rhombic link which includes, as its component sides, a portion of said guide rod and a portion of the link element of said first parallel link of which opposite summits are an arthrosis including said drive shaft and a rotary joint of said slider.
The transfer arm of the present invention which can accomplish the second object exhibits effects of accurately transferring substrates and keeping clean operational environment because of little wearing of components so as to obtain excellent durability. Since all of components can be heat resisting members, the transfer arm of the present invention can be used under high temperature condition. Further, since bearings with solid lubricant are used for the respective arthroses, the transfer arm can be used under ultra-high vacuum condition.